Although insulin has profound effects on the metabolism of many tissues, the mechanism(s) through which insulin regulates intracellular processes is not understood. In our previous studies we demonstrated that insulin, a polypeptide hormone, entered the interior of target cells and bound to intracellular structures including the nucleus and endoplasmic reticulum. In the present proposal, we plan to further characterize the nature of the intracellular binding sites for insulin in rat liver, including the solubilization, electrophoretic mobility, and immunoreactivity of these proteins. In addition, the status of cell surface and intracellular binding sites for insulin will be examined in animals in various states of insulin resistance. Further we plan to determine the metabolic importance of this internalization process. One series of studies employing cultured rat hepatoma cells will use both cell fusion and liposome techniques. Another series will employ subcellular fractions of normal liver to determine if insulin regulates nuclear ATPase and RNA polymerase activities as well as ribosomal protein synthesis.